In a systematic review article published on October 3, 2022, in the journal Science of the Total Environment, Gurusamy Kutralam-Muniasamy from the Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico, and co-authors summarized the current scientific data on microplastics in human biological samples. The authors searched Pubmed/Medline, Scopus, and Web of Science databases, for peer-reviewed articles published until August 1, 2022, using the terms microplastics and human, blood, placenta, saliva, colon, hair, liver, kidney, lungs, sputum, feces, or breast milk.
A total of 20 articles fit their inclusion criteria of which 80% were published in 2021 or 2022. The review showed that studies have analyzed a wide range of human biological samples, including blood, breastmilk, lung, bronchoalveolar lavage fluid, liver, kidney, spleen, placenta, meconium, hair, head, hand, face, skin, saliva, colectomy specimens, sputum, and feces. Feces is the biological sample type that has been investigated the most included in 30% of the studies.
Moreover, Kutralam-Muniasamy et al. summarized that as of August 2022 microplastics have been detected in 15 biological components with microplastics’ prevalence greatly varying between them. While in 13 components the prevalence was 100%, it was low in feces (40-60%) and no particles have been found in the kidney so far. Reported microplastic concentrations ranged from 0-2.72 particles/g breastmilk (FPF reported), 3 particles/g placenta and meconium (FPF reported and here), and 28 particles/g colon. Studies further indicate that microplastic concentrations are higher in individuals with health issues compared to those with none but “further investigations are critical to extensively evaluate whether microplastic accumulation represents a potential cause of the disease or that disease exacerbates the retention of microplastics.” Overall, fibers and fragments were the predominant shape of microplastics in human biological samples and sizes ranged from ≥ 700 nm to 5 mm. One source of human exposure to microplastics is via food and beverages with a previous study having summarized the respective exposure concentrations (FPF reported).
Kutralam-Muniasamy and co-authors further provided an overview of the studies’ applied approaches to sample, isolate, detect, and characterize microplastics. Findings included that spectroscopic techniques were the most frequent method applied for microplastic identification and quantification (17 out of the 20 studies). Based on the literature review, the scientists outlined current challenges and solution options. One issue described is the cross-contamination of samples leading to a falsification of results. According to the authors, different contamination prevention measures have been employed but it would be critical for further research to “ follow a consistent plastic-free contamination control process” to generate more robust and representative data. In their review they present important steps to be included in that process. Furthermore, they expressed the need to also develop a standardized protocol to study microplastics in each human biological sample. The researchers concluded that significant knowledge gaps exist on the reviewed topic and that especially more quantitative studies with individuals outside Europe and studies on nanoplastics would be needed.
A study published in the journal Environmental Science and Technology on October 21, 2022, and thus after the review Kutralam-Muniasamy et al. conducted, also looked at microplastics in human samples. In the article, Shaojie Liu from Fudan University, Shanghai, China, and co-authors described the occurrence of microplastics in placenta and meconium samples and possible effects on human microbiota. The scientists collected meconium and placenta samples from 18 mother-infant pairs in Shanghai, China, in 2021.
They detected 16 types of microplastics with polyamide and polyurethane being the most dominant (78%). Counting particles with diameters between 20 and 500 µm, the median concentration of microplastics was found to be 18 particles/g and 54 particles/g for placenta and meconium, respectively. The assessment of the microbiota genera in placenta and meconium showed that polystyrene “may affect the diversity of meconium microbial communities” corresponding to findings previously reported for mice gut microbiota (FPF reported). In addition, polyethylene concentration “was inversely correlated with Bacteroidetes” and “many other genera of placenta microbiota.” Overall, the study indicates that high microplastic concentrations can impact microbiota genera in the placenta and meconium. However, Liu et al. emphasized that their study has some limitations such as relatively small sample size and potential contamination of samples with microplastics.
In another review article published on October 10, 2022, in the journal Toxics, Nur Hanisah Amran and co-authors from the Universiti Putra Malaysia, Selangor, Malaysia, focused on compiling the current evidence of microplastics exposure during the early developmental stage and the associated effects. The authors pointed out that children have been reported to consume between 553 particles/day in total to up to 4,550,000 particles/day only through feeding bottles. This wide range would indicate the uncertainties in microplastic exposures during early life as well as the analytical challenges. The review summarizes the effects of microplastics exposure on the digestive system, the reproductive system, the central nervous system, the immune system, and the circulatory system during early developmental stages. Apart from a few exemptions all of the studies were conducted in mice. Amran and co-authors concluded that their review of “early life microplastics exposure presents grounds of concern” but also that “foundational research on children’s exposure to microplastics is severely lacking”.
The AURORA project aims to contribute new scientific findings on that topic by analyzing the effects of micro- and nanoplastics on early life health (FPF reported).
References
Kutralam-Muniasamy, G. et al. (2022). “Microplastic diagnostics in humans: “The 3Ps” Progress, problems, and prospects.” Science of the Total Environment. DOI: 10.1016/j.scitotenv.2022.159164
Liu, S. et al. (2022). “The Association Between Microplastics and Microbiota in Placentas and Meconium: The First Evidence in Humans.” Environmental Science and Technology. DOI: 10.1021/acs.est.2c04706
Amran, N. H. et al. (2022). “Exposure to Microplastics during Early Developmental Stage: Review of Current Evidence.” Toxics. DOI: 10.3390/toxics10100597
